1. Technical Field
The invention relates to the field of night vision devices that enable a viewer to observe objects at night or during other low-light conditions. More particularly, this present invention relates to a system for gauging distances between objects under low light conditions.
2. Background Art
Night vision devices (NVD) are well known. A common type of a night vision device is based on an image intensification technology and is used to provide soldiers, aviators, and sailors with the ability to view objects at night or during other low light conditions.
A common scenario associated with the use of a night vision device is a soldier using a night viewer, such as a night vision goggle (xe2x80x9cNVGxe2x80x9d) AN/PVS-7 or others, to observe a battlefield scene at night. If the night-time battlefield scene includes people sitting in a vehicle, it is likely that at some point the vehicle occupants will need light to illuminate their compartment to complete operations. Unless otherwise protected, the light source will cast a glow that is visible to the observer outside the vehicle. To prevent or minimize observation by an xe2x80x9cunfriendlyxe2x80x9d soldier using a NVG, a xe2x80x9cblackout mode of operationxe2x80x9d has been adopted to counteract the observation advantages that the xe2x80x9cunfriendlyxe2x80x9d NVG equipped soldier may have on the battlefield. Consequently, this scenario has prompted a concern with the tactical risk associated with any lighting used in the night vision goggle (xe2x80x9cNVGxe2x80x9d) blackout mode of operation.
The military has recognized a problem with night vision imaging devices typified in the PVS-7 NVIS (Night Vision Imaging Systems), substantially manifested by vehicle impacts between a leading and trailing vehicle in a convoy. This is commonly called a xe2x80x9cRear-End Collisionxe2x80x9d and frequently results in a series of collisions between multiple vehicles in a convoy.
Another scenario associated with use of night vision devices by military pilots is flying in formation in-route or for take-offs and landings. It is desirable for helicopter pilots to maintain precision position relationships of 3 to 5 rotor disk spacings, typically 150 to 250 feet, during in-route formation flying and also 1 to 3 rotor dick spacings during take-offs and landings, typically 50 to 150 feet.
It is recognized that NVIS devices suffer from an inherent deficiency with human depth perception by the users of devices like the PVS-7 and similar. The depth perception problem has been recognized and historically has been addressed by reducing convoy speeds and increasing required spacing between vehicles. Military wide orders have been directed to NVIS convoy operators to maintain a low speed. Vehicle spacing varies depending upon logistic or command procedures of each Battalion or group.
A low speed limit for night convoy operations increases susceptibility to enemy detection and increases exposure time to enemy threats. Any effective increase in speed would reduce the convoy""s exposure time, and reduce the probability of detection by the enemy at any point outside of the hearing range of the convoy.
Statements have been issued having an objective to increase the pace of battlefield operations beyond the enemy""s ability to react, along with a requirement to maintain operations in the nighttime battlefield.
To accomplish these objectives, a completely new method has had to be developed to accomplish enhanced convoy operations, while maintaining safe convoy and troop movements during the night.
A number of alternative methods can be examined, including acoustic sonic measuring techniques, where an acoustic pulse is emitted and the time measured for an echo to return to the device. This time delay can be used to accurately determine the distance between vehicles or objects. The primary problem with this strategy is it generates a signal which can be detected by the enemy, thus increasing the susceptibility for the convoy to be targeted and destroyed.
Similar strategies could be developed using lasers or other wavelengths of generated signals and in each case creating a detection risk to the convoy from the enemy.
For aviation purposes landing systems using combinations of lights have been used to indicate proper glide slopes to pilots during final approaches to landing. A combination of lights or lenses have been used to project a different indication of lights to the approaching pilot depending on the pilot""s relative position to the standard glide slope when viewing the indicator device.
Also, observers for artillery have used binocular type devices having indicators to help the observer determine relative distances for targets.
While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.
In accordance with the present invention, a reticle adapter for judging distance from an object is used with a viewing apparatus to detect relative positions of signals from at least two spaced apart marker devices formed on a first object. An image of the relative positions of the markers is created within a field of view. A reticle projecting member is removably mounted on the viewer. The reticle projector forms a reticle signal superimposed on the field of view at the scene input end of the viewer. The reticle is selected to form a control area within which simultaneous appearance of at least two images of the spaced apart markers indicates that the first object is at a distance at least as great as a desired distance from the viewer. Simultaneous appearance of less than two images of the spaced apart markers within the control area indicates that the first object is at a distance less than the desired distance.
These and other objects, advantages and features of this invention will be apparent from the following description taken with reference to the accompanying drawings, wherein is shown the preferred embodiments of the invention.